Television receiver



Dec. 29, 1942. A. H. ROSENTHAL 2,306,407

TELEVISION RECEIVER Filed March 11, 1939 fin/(afar terials belong to theclass of the Patented Dec. 29, 1942 2,306,407 TELEVISION RECEIVER AdolfHeinrich Rosenthal. Kensington, London,

England, assignor,

Scophony Oorporatio by mesne assignments, to

n of America, a corporation of Delaware Application March 11, 1939,Serial No.

New York,

Great Brltain March 18, 1938 Claims. (Cl. 178-75) The present inventionrelates to television receivers. and is a continuation in part of mycopending application Serial No. 253,182 filed January 27, 1939, whichis concerned with a novel form of image screen for a televisionreceiver. By the term image screen is meant a screen, the opticalproperties of which change from point to point in accordance withreceived picture signals. so that such a screen can be imaged with theaid of light from an external source on to a projection screen to give arepresentation of the picture.

If certain crystals. which are normally transparent to visible cathoderays, x-rays. radium rays or by light of a suitable wave length, adeposit of opaque materlal, which is constituted by what willhereinafter be referred to as "opacity centres, is created in thiscrystal, the degree of opacity depending on the intensity of theincidentradiation. Examples of such crystals are many of the alkali and alkalineearth halides, such as the chlorides, bromides and idodides ofeodium andpotassium, lithium bromide, calcium fluoride, and strontium fluoride andchloride: and also certain silver salts such as silver bromide. Allthese maso-called "ionic crystals." 1. e. crystals in which there arepositive and negative components, and the forces that hold them togetherare electrostatic, at least in part. In the case of the alkali halidecrystals research has indicated that the opacity centres probablyconsist of neutral alkali atoms which are loosely bound in the interiorof the crystals in some manner or other, and which are similar to thedeposit of metallic silver in a latent photographic image. The depositof metal in the crystal latticecan also be created by heating an alkalihalide crystal in an atmosphere of the vapour of its alkali metal, whichdiffuses in the crystal.

Once formed, the opaque deposit can also be destroyed by the abovementioned rays, the amount of destruction in a given time intervaldepending on the intensity of the rays and on the density of the depositalready formed. Thus the gross effect of any given intensity of theincident radiation, being the result of an equilibrium between theformation and destruction of the deposit. may be an increase of thedeposit for low intensities and a decrease for the high intensities, ina manner similar to the well known "Solarisation" of the latentphotographic image. Thus, over a range of low intensities of theincident radiation, increase in intensity will result light, are struckby a beam of in an increase of the deposit. whilst over a range of highintensities an increase in intensity will result in a decrease of thedeposit.

The materials exhibiting this property may be defined as those of theionic type in which the injection of electrons into the crystal latticecan give rise to an opaque deposit in said lattice.

In the co-pending application referred to above there is contemplatedthe use of a transparent crystalline material oi the type deflnedlntheimage screen of a television receiver. The material may be in the formof a single flat crystal, a mosaic of small crystals, or amicro-crystalline structure. A composite crystal or a mixture of two ormore or such crystalline materials may be used.

In most cases, and particularly when the materialisintheformofasinglecrystaLadisappearitnceof the opaque deposit can be produced thecrystal in an electric neldand temperature, in which case the deposit isdrawn through the crystal towards the positive pole producing theelectric field. when it reaches the positive pole is disappears, leavingthe crystal substantially transparent. The speed of movement of thedeposit depends upon the strength of the field and upon the temperature,and can be varied within wide limits by varying either magnitude. For aElven field strength this speed of movement increases with thetemperature of the crystal.

In the various embodiments described in the co-pending applicationreferred to above. conditions are such that the opaque deposit in theimage screen constitutes in itself a visible image, and consequentlythis image can be directly pro- ,iected on to a proiection screen.

The formation of opacity centres at any given elemental area of thescreen is accompanied by a corresponding change in the refractive indexof this area, with respect to the refractive index of tion of electronsand the remaining areas, due to the temporary liberathe presence it freeor looseiy bound electrons in the substance of the screen. Instead oi,or in addition to, the changes in opacity of the screen these changes inrefractive index can be utilized to produce a visible image, and it isan object of the present invention to provide means whereby thisutilization of the changes of refractive index can be achieved.

According to the present invention a television receiver comprises aimage screen of a material of the type defined, means for scanning thescreen with a beam of radiant energy modulated in intensity inaccordance with the received picture signals to produce a change in therefractive index of the material of each elemental area in turn, thedegree of change depending upon the instantaneous intensity, of the beamstriking the area, means for illuminating said image screen, opticalmeans for separating the portion of the light which undergoes a changeof direction due to said change in refractive index from the remainingportion, and means for directing one of said portions on to a projectionscreen.

The chiei advantage of the present invention is that where theconditions are such that the density or tint oi the opaque deposit arenot suitable for the production of a satisfactory visible picture, themethod of the present invention can be used to overcome this difiiculty.

The invention will now be described by way of example with reference tothe accompanying drawing in which Fig. 1 shows schematically one form ofthe invention, and

Fig. 2 shows an alternative form of construction of the image screen.

Referring to Fig. l, a cathode ray tube l is provided with a cathode 2,a control grid I, a, beam focussing coil 4, deflecting coils 5, ii andan accelerating anode 1. Picture signals irom 8 are applied between thecathode and control grid in such a way that the positive potential ofwith increase in signal strength, so that a modulated beam is producedand is swept over the image screen in the usual manner. The image screenconsists of a flat crystal 9 of an alkali halide such as potassiumchloride, provided on each side with an electrode Ill. ll designed topermit the passage of light. These electrodes are shown in the form ofthin transparent sputtered metallic layers, also be in the term of finemeshes The potential of the electrode II is maintained positive withthat or the electrode It to provide an electric field in the crystal.

As explained in detail in the co-pendins application referred to above afugitive image in the iorm of an opaque deposit is produced in thecrystal which travels through the crystal and disappears at theelectrode H, and normally it is possible in project this image directlyon to a receiving screen. The formation of this image is accompanied bya corresponding change in the refractive index of the crystal. thischange, for any given elemental area of the crystal depend in! upon theintensity of the cathode ray beam when it strike the area.

According to the present invention, this change in the refractive indexis also utilized in forming a visible image on receiving screen. In Fig.1 the so-called Tlipler-Schlieren method is used tor this purpose, andto this end the condenser lens system It forms an image of the lightsource It on the opaque bar ll, so that in the absence of any changes inthe refractive index of the crystal 9, no light proceeding from thecrystal can pass the bar ll.

1! now a change in the refractive index, and hence a change in theoptical path through the material iorming a given elemental area of thecrystal is produced, the light rays passing through this area willexperience a change of direction, so that some of the light will passthe bar ll. This light is utilized by the projection lens I! to form animage of the crystal surface on the projection screen it.

for the signal In order to obtain a satisfactory picture on theprojection screen it it is necessary that the quantity of lightproceeding irom a given elemental area of the crystal which passes thebar i4 should be substantially proportional to the intensity or theradiant energy producing the change in the optical path in the elementalarea, since it is this quantity of light which determines the intensityof the corresponding elemental area of the picture on the screen it. Nowthis quantity of light is not proportional to the optical path throughthe elemental area under consideration but is proportional to the firstdifferential of this, i. e. if 1/ represents the geometrical paththrough the crystal (if the light is incident normally on the crystal uwill represent the thickness of the crystal) if n represents therefractive index of the material of the elemental area, and if .1:represents any linear dimension of the area in the plane of the crystal,then yn gives the optical path and the quantity of light passing the barIt is proportional to sin- (13 This latter expression will behereinafter referred to as the gradient of the optical path.

This gradient along the screen surface in the optical path through eachelemental area of the screen may be produced by modulating the intensityof the scannins beam with high frequency oscillations derived from thesource It, the frequency of these oscillations being in theneighbourhood of element frequency. so that there is produced a gradientin the rciractive index of the crystal in the line scanning directionover each elemental area, and hence a gradient in the optical path. Thisgradient is then altered by the signal modulations superimposed on thehigh frequency modulations. This effect can also be produced by using anunmodulated beam (except modulations) and interposing a flne metallicgrating (ill, Fig. 8) at or near the scanned suriace oi the crystal, orsuch a grating may be in the form of a partly transparent inetallicdeposit on the crystal surface and acting at the same time as one of thecrystal electrodes.

Alternative methods of producing the desired changes in refractive indexin the image screen are substanmethods of producing the opaque depositin the screen which are described in detail in the coending applicationreferred to above, and need not be described in the presentspecification.

I claim as my invention:

1. A television or like receiver comprising a cathode ray tube, an imagescreen in said tube comprising a material of the ionic crystal glass andof the type in which the injection of electrons into the crystal latticecan give rise to an opaque deposit in said lattice, means formoduscreen, a light source for illuminating and caus ing light to passthrough said screen, an optical stop on the side of said screen remotefrom said light source, an optical system adapted to form an image 0!said light source on said stop, and optical means for utilizing lightwhich undergoes a change in intensity in passing through said screen asaresult of the opacity thereof, and which passes said stop to term animage of said screen on a projection screen.

3. A television or like receiver comprising a cathode ray tube, an imagescreen in said tube comprising a material or the ionic crystal class andof the type in which the injection of electrons into the crystal latticecan give rise to an opaque deposit in said lattice, a grating on saidscreen, means for modulating the cathode ray beam in accordance withreceived signals and for causing it to scan said screen, a light sourcefor illuminating and causing light to pass through said screen, anoptical stop on the side or said screen remote from said light source,an optical system adapted to form an source on said stop, and opticalmeans for utilizing light which undergoes a change in intensity inpassing through said screen as a result of the opacity thereof, andwhich passes said stop to form an image said screen on a projectionscreen.

, 3. A television or like receiver as claimed in claim 2 wherein saidgrating is in the term of a partly transparent metallic deposit on said4. A television or like receiver comprising a cathode ray tube, an imagescreen in said tube comprising a material oi the ionic crystal class and01' the type in which the injection oi electrons into the crystallattice can give rise to an opaque deposit in said lattice, a source ofhigh irequency oscillations, means for modulating the cathode ray beamin accordance with said high frequency oscillations from said source andwith received signals, and means for causing said beam to scan saidscreen, a light source i'or illuminating and causing light to passthrough said screen, an optical stop on from said light source, anoptical system adapted image at said light to form an image of saidlight source on said p. and optical means for utilizing light whichundergoes a change in intensity in passing through said screen as aresult of opacity thereof, and which passes said stop to form an imageof said screen on a projection screen.

5. In a television receiver, the combination comprising an image screenof a material or the ionic crystal class and of the type in which theinjection 0! electrons into the crystal lattice can give rise to anopaque deposit in said lattice, means for scanning said screen with acathode ray beam, a source oi high frequency oscillations, means formodulating said cathode ray beam with said oscillations so that saidbeam produces over each elemental area a gradient in the optical paththrough the material of said element, said cathode ray beam beingfurther modulated in intensity in accordance with received picturesignals, and adapted to produce a modulation of the gradient of theoptical path for each elemental area of the screen in turn, the degreeof this modulation depending upon the instantaneous intensity of thebeam striking the area, a light source for illuminating and causinglight to pass through said screen, an optical stop on the side of saidscreen remote from said light source, an optical system adapted to terman image or said light source on said stop, and optical means forutilising light which undergoes a change in intensity in passing throughsaid screen due to said modulation oi the gradient of the optical pathfrom the remaining portion and which passes said stop to form an imageof said screen on a the side oi said screen remote 5 projection screen.

ADOLF HEINRICH ROSENTI-IAL.

